16. Magnetism and Electromagnetism

Question 1

What are the properties of magnets?

Answer 1

1. Strongest at its’ poles
2. Like poles repel, unlike poles attract
3. Freely suspended magnet comes to rest in the North South direction
4. Magnetic North and South poles always occur in pairs
5. Attract Magnetic Material

Question 2

Explain what Induced Magnetism is

Answer 2

• It can take place when a magnetic material is placed closed to a stronger magnet or within a current-carrying solenoid

Question 3

What are the 2 methods to make a magnetic material a magnet

Answer 3

1. By stroking it with a strong magnet
2. By placing the magnetic material inside the current-carrying solenoid.

Question 4

How to demagnetise a magnet by hitting or heating the magnet

Answer 4

• By placing the magnet due east-west direction minimises the influence of the Earth’s magnetic field during the process

Question 5

How to demagnetise a magnet by alternating current?

Answer 5

• By placing the magnet inside a solenoid, and gradually reduce current to zero.

Question 6

What are temporary magnets?

Answer 6

They retain their magnetism in the presence of an electric current or a permanent field strength

Question 7

What are permanent magnets?

Answer 7

Permanent magnets do not require the presence of an electric current or a permanent magnetic field to retain their magnetism

Question 8

Compare soft and hard magnetic materials

Answer 8

1. Soft magnetism material is easily magnetised and demagnetised. Commonly use as temporary magnets such as electromagnets in junkyards
2. Hard magnetism material is difficult to magnetised and demagnetised. Commonly use as permanent magnets such as magnetic recording media

Question 9

What are the characteristic of magnetic field lines?

Answer 9

1. They never cross each other
2. They are continuous and form closed loops
3. Distance between magnetic field lines represents the strength of magnetic field

Question 10

Describe the magnetic field when there is no current in straight wires?

Answer 10

• The needles of the compasses come to rest in the north-south direction

Question 11

Describe the magnetic field when there is a large current in straight wires?

Answer 11

-The needles of the compasses immediately defect and form a circle around the conductor

Question 12

What does right-hand grip rule help to determine?

Answer 12

1. The direction of the thumb pointing to is where convectional current is present
2. Where the curl of the fingers determines the direction of the magnetic field

Question 13

What are the factors of a strong magnetic field of a solenoid?

Answer 13

1. When the numbers of turn per metre is high
2. When the current flowing in solenoid is high
3. When a soft iron core is added

Question 14

What causes a motion?

Answer 14

1. When magnetic field interact with another magnetic field
2. Attraction or repulsion takes place
3. Where the attraction and repulsion are large enough, they cause motion
4. Also known as catapult effect

Question 15

How can the force be determined by the Flamming’s Left hand rule

Answer 15

1. Where the thumb represents the force
2. Forefinger determines where the Nort Pole is
3. Middle finger determines the current flow

Question 16

What does the cross and dot represent in terms of current

Answer 16

1. Cross represents current flowing in
2. Dot represents current flowing out